Question

Abe has a bag of marbles and wants to divide them into sets. The first set will have 2 marbles; the second set, 5; the third set, 8; the fourth set, 11; and so on. How many sets will he have if he starts with 40 marbles?

Answer 1

Well.. Let's first list the number of marbles in each sets:
2,5,8,11...etc How many sets will he have if he starts with 40 marbles?
If we look at the increasing sets. What pattern do you notice? By what amount do each set increase by? Now if you have 40 marbles, tally how many sets you have as you remove the number of marbles in each set.